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Firmicutes: The Low G + C Gram-Positive Bacteria 1 23 Copyright © McGraw-Hill Global Education Holdings, LLC. Permission required for reproduction or display.

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Presentation on theme: "Firmicutes: The Low G + C Gram-Positive Bacteria 1 23 Copyright © McGraw-Hill Global Education Holdings, LLC. Permission required for reproduction or display."— Presentation transcript:

1 Firmicutes: The Low G + C Gram-Positive Bacteria 1 23 Copyright © McGraw-Hill Global Education Holdings, LLC. Permission required for reproduction or display.

2 Genus Clostridium… Great practical importance –food spoilage through the Strickland reaction (oxidation and reduction of amino acids to organic acids) –industrial production of butanol –toxin production (botulinum toxin) –endospore formers 2

3 Important Species of Clostridium C. botulinum –food spoilage (especially canned foods); botulism C. tetani – tetanus C. perfringens – gas gangrene, foodborne illness C. difficile – important nosocomial infection –post antibiotic infection (CDAD), pseudomembranous colitis C. acetobutylicum - manufacture of butanol 3

4 Botulism Caused by Clostridium botulinum, an obligately anaerobic, endospore-forming, Gram-positive rod –on Select Agent List (agents that pose a severe threat – CDC) Most common source of infection is insufficiently heated home-canned food –endospores not killed, then germinate and produce toxin –if food inadequately cooked, toxin remains and causes disease 4

5 Botulism Botulinum toxin –neurotoxin that binds to synapses of motor neurons Diagnosis –restricted to reference laboratories –demonstration of toxin in patient’s serum, stool, or vomitus or C. botulinum in stool cultures 5

6 Botulism Infant botulism (most common form) –endospores ingested, germinate, reproduce, and produce exotoxin (stomach not acidic) –constipation, listlessness, general weakness, and poor appetite; death may result from respiratory failure Treatment, prevention and control –symptomatic/supportive therapy and administration of antitoxin –safe food processing practices and not feeding honey to babies under one year of age 6

7 Tetanus Caused by Clostridium tetani –anaerobic, Gram-positive spore-former endospores found in soil, dust, hospital environments, and mammalian feces –produces tetanospasmin in low oxygen tension environments causes prolonged muscle spasms –also produces tetanolysin, a hemolysin Portal of entry – skin wounds (puncture wounds most susceptible) 7

8 Tetanus Clinical manifestations –early in disease – tension or cramping and twisting of skeletal muscles and tightness of jaw muscle –advanced disease – trismus (“lockjaw”), characteristic facial expressions, board-like rigidity of trunk, tonic convulsions, and backward bowing of back –death usually results from spasms of diaphragm and inter- costal respiratory muscles 8

9 Tetanus Diagnosis –clinical history of wound infection and muscle stiffness Treatment, prevention, and control –antibiotic therapy and treatment with antitoxin –active immunization with toxoid (DPT vaccine), and proper care of wounds contaminated with soil, prophylactic use of antitoxin 9

10 Gas Gangrene or Clostridial Myonecrosis Most commonly caused by Clostridium perfringens –Gram-positive, spore-forming rod –produce gas gangrene, a necrotizing infection of skeletal muscle or clostridial myonecrosis –secretes toxin and tissue damaging enzymes Transmitted by contamination of injured tissue by spores from soil or bowel microbiota 10

11 Gas Gangrene Clinical manifestations –severe pain, edema, drainage, muscle necrosis Diagnosis –recovery of appropriate clostridial species and characteristic disease symptoms Treatment, prevention, and control –surgical debridement, administration of antitoxin, antibiotic therapy, and hyperbaric oxygen therapy –prompt treatment of all wound infections and amputation of limbs 11

12 Antibiotic-Associated Colitis (Pseudomembranous Colitis) Clostridium difficile (C. difficile associated diarrhea – CDAD) –uncomplicated diarrhea –pseudomembranous colitis viscous collection of inflammatory cells, dead cells, necrotic tissue, and fibrin that obstructs the intestine –toxic megacolon inflammation resulting in intestinal tissue death 12

13 Clostridium difficile Anaerobic spore forming bacillus found in the intestines of some healthy people –numbers are kept in check by other normal intestinal microbiota –excessive antibiotic use eliminates normal microbiota and allows C. difficile to overgrow most common are amoxicillin, ampicillin, clindamycin, cephalosporins –increasing due to use of hand sanitizers 13

14 C. difficile Virulence Factors C. difficile multiplies and produces toxins –toxin A (enterotoxin causing diarrhea) –toxin B (cytotoxin kills cells) Inflammation, diarrhea, fever, nausea, cramping Most common cause of diarrhea in hospitalized patients Treatment is with antibiotics 14

15 Genus Bacillus Motile, peritrichous flagella, usually aerobic, catalase positive Various species produce antibiotics Bacillus subtilis is type species –Gram-positive, facultative anaerobe –soil-dwelling, spore forming –may develop biofilms 15

16 Bacillus subtilis Used as model organism for –gene regulation, cell division, quorum sensing, cellular differentiation Genome was one of first to be sequenced –families of genes expanded by gene duplication –18 genes for sigma factors –  10 integrated prophages or remnants of prophages 16

17 Other Important Species of Bacillus B. cereus – food poisoning B. anthracis – anthrax B. thuringiensis and B. sphaericus – used as insecticide for years 17

18 Anthrax Caused by Bacillus anthracis (Select Agent) –Gram-positive, aerobic, endospore-forming –endospores viable in soil and animal products for decades –plasmid encodes genes for anthrax toxin Transmitted by direct contact with infected animals or their products –portal of entry determines form of disease Potential bioterrorism agent 18

19 Anthrax Virulence B. anthracis evades immune system by –capsule which inhibits phagocytosis – synthesis of complex exotoxin protective antigen – forms hole for entry of other toxins edema factor – fluid release and edema lethal factor – inhibits cytokine production –macrophages die, release toxic contents leading to septic shock, death 19

20 Cutaneous Anthrax Infection through cut or abrasion of skin Clinical manifestations –1 to 15 day incubation –skin papule that ulcerates (eschar), headache, fever, and nausea Antibiotic therapy 20

21 Pulmonary and Gastrointestinal Anthrax Pulmonary anthrax –woolsorter’s disease –inhalation of endospores –resembles influenza –if bacteria reach the bloodstream, usually fatal Gastrointestinal anthrax –ingestion of endospores 21

22 Anthrax Diagnosis –presumptive ID in sentinel labs of Laboratory Response Network (LRN) Gram-stained smear of skin lesion, cerebrospinal fluid or blood; also growth and biochemical characteristics of culture –confirmatory diagnosis by PCR and serology Treatment, prevention, and control –antibiotic therapy and symptomatic/supportive therapy –immunization of animals and persons at high risk 22

23 Genus Sporosarcina Only known endospore - former that has coccoid and not rod shape Tolerates pH up to 10 –degrades urea to ammonia and carbon dioxide Isolated from agricultural soils where animals urinate 23

24 Family Staphylococcaceae 5 genera, includes Staphylococcus Facultatively anaerobic, nonmotile, Gram-positive cocci Usually form irregular clusters Normally associated with warm-blooded animals in skin, skin glands, and mucous membranes 24

25 Members of Staphylococci S. aureus – coagulase positive, pathogenic S. epidermidis – coagulase negative, less pathogenic but nosocomial opportunists Many pathogenic strains are slime producers Teichoic acid and peptidoglycan contribute to pathogenicity 25

26 Staphylococcal Diseases Caused by members of the genus Staphylococcus –Gram-positive cocci, occurring singly, in pairs, tetrads, or grape-like clusters –facultative anaerobes and usually catalase positive –normal inhabitants of upper respiratory tract, skin, intestines, and vagina 26

27 Staphylococcal Diseases Harbored by asymptomatic carriers or active carriers (have the disease) –spread by hands, inanimate objects or expelled by respiratory tract, or through blood May produce disease in almost every organ and tissue Immune compromised most at risk 27

28 Virulence Factors of Staphylococci Exotoxins and enzymes involved in invasiveness Toxin genes may reside on plasmids and on chromosome Examples –enterotoxin – food intoxication –bacteremia and abscess formation 28

29 29

30 Staphlococcus aureus Most important human staphloccoccal pathogen –e.g., abscesses, boils, wound infections, pneumonia, toxic shock syndrome –major cause of common food poisoning Virulence factors –coagulase which causes blood plasma to clot –the toxin β-hemolysin lyses cells 30

31 Staphylococcal Food Poisoning Results from ingestion of improperly stored or cooked food (e.g., ham, processed meats, chicken salad, ice cream, and hollandaise sauce) in which Staphylococcus aureus has grown and released enterotoxin Bacteria produce heat-stable enterotoxins in food –properly cooking the food will not destroy toxin; intoxications can result from thoroughly cooked foods Symptoms include abdominal pain, cramps, diarrhea, vomiting, and nausea 31

32 Staphylococcal Food Poisoning Diagnosis –based on symptoms or laboratory identification of bacteria from food –enterotoxins can be detected in foods by animal toxicity tests Treatment, prevention, and control –fluid and electrolyte replacement –avoidance of food contamination, and control of personnel involved in food preparation and distribution 32

33 Staphylococcal Scalded Skin Syndrome (SSSS) Caused by strains of S. aureus that carry a plasmid-borne gene for exfoliative toxin (exfoliatin) Epidermis peels off revealing red area underneath Diagnosis –isolation/identification of Staphylococcus involves commercial kits 33

34 Staphylococcal Scalded Skin Syndrome (SSSS) Treatment, prevention, and control –isolation and identification based on catalase test, coagulase test, serology, DNA fingerprinting, and phage typing –antibiotic therapy many drug-resistant strains –personal hygiene, food handling, and aseptic management of lesions 34

35 Toxic Shock Syndrome (TSS) Caused by S. aureus strains that release toxic shock syndrome toxin and other toxins Some cases occur in females who use superabsorbent tampons Disease results from body’s response to staphylococcal superantigens Clinical manifestations –low blood pressure, fever, diarrhea, extensive skin rash, and shedding of skin 35

36 Staphylococcal Lesions Localized abscess –S. aureus infects a hair follicle, tissue necrosis results –coagulase is produced forming a fibrin wall around lesion, limiting spread –liquefaction of necrotic tissue in center of lesion occurs; abscess spreads –may be a furuncle (boil) or carbuncle –bacteria may spread from area via lymphatics or bloodstream 36

37 Methicillin-Resistant Staphylococcus aureus (MRSA) S. aureus isolates that are resistant to β-lactam antibiotics (penicillins and cephalosporins) Community acquired (CA) – MRSA –healthy individuals not recently hospitalized –associated with serious and fatal infection –may also be acquired in health care setting 37

38 S. aureus Antibiotic Resistance Methicillin-resistant S. aureus (MRSA) and Vancomycin resistant S. aureus (VRSA) –among most threatening antibiotic resistant VRSA may have no treatment –obtained from genetic elements received from other organisms –virulence factors also acquired from mobile genetic elements 38

39 Slime Producers (SP) Produced by pathogenic strains of Staphylococcus –a viscous extracellular glycoconjugate –allows bacteria to adhere to smooth surfaces and form biofilms –Inhibits neutrophil chemotaxis, phagocytosis, and antimicrobial agents 39

40 Staphylococcus epidermidis Common skin resident Sometimes responsible for endocarditis and for infections of patients with lowered resistance –e.g., wound infections, surgical infections, and urinary tract infections 40

41 Genus Listeria Wide distribution in nature - common in decaying matter L. monocytogenes pathogen of humans and animals –listeriosis - food-borne infection –especially dangerous to pregnant women, the fetus and infant, and compromised individuals (90% of cases) –1600 cases/yr in US, 3 rd leading cause of fatalities associated with food-borne illnesses –grows at refrigeration temperatures –associated with many foods that are not cooked, i.e lunch meats, cheeses, sprouts, fruits 41

42 Order Lactobacillales Also called lactic acid bacteria (LAB) Morphologically diverse –nonsporing –usually nonmotile Ferment sugars for energy –lack cytochromes –fastidious Contains several important genera 42

43 Genus Lactobacillus Widely distributed in nature –on plant surfaces –in dairy products, meat, water, sewage, beer, fruits, and other materials –normal flora of mouth, intestinal tract, and vagina usually not pathogenic 43

44 Importance of Lactobacilli Fermented products –vegetable products (sauerkraut, pickles, and silage) –beverages (beer, wine, juices, milk) Sour dough bread Swiss cheese and other hard cheeses, yogurt Sausages L. acidophilus – sold as probiotic agent Food spoilage – beer, wine, milk, meat 44

45 Importance of Leuconostoc Wine production Production of sauerkraut and pickles Production of buttermilk, butter, and cheese Synthesis of dextrans (L. mesenteroides) Involved in food spoilage –tolerate high sugar concentrations –grow in heavy syrup 45

46 Families Streptococcaceae and Enterococcaceae Chemoheterotrophic, mesophilic, nonsporing cocci, usually nonmotile Fermentative only Aerotolerant and anaerobic Groups –enterococci –lactococci –streptococci 46

47 Three Groups of Streptococci Pyogenic (pus producing) streptococci –e.g., S. pyogenes – streptococcal sore throat, acute glomerulonephritis, and rheumatic fever Oral streptococci –e.g., S. mutans – dental caries Other streptococci –e.g., S. pneumoniae – lobar pneumonia and otitis media 47

48 Streptococcal Diseases Caused by strep, group of Gram-positive bacteria –Streptococcus pyogenes one of most important pathogens group A β-hemolytic streptococci (GAS) –virulence factors extracellular enzymes that break down host molecules streptokinases – dissolve clots streptolysin O and S – kill host leukocytes capsules and M protein for attachment 48

49 Streptococcal Diseases Streptococcus pyogenes –widely distributed, some carriers –common infection “Strept throat” –transmission respiratory droplets, direct or indirect contact Diagnosis –based on clinical and laboratory findings –rapid diagnostic tests available 49

50 Streptococcal Pharyngitis Common infection called strep throat Spread by droplets of saliva or nasal secretions Infection in throat (pharyngitis) or tonsils (tonsillitis) Signs and symptoms of disease not diagnostic because many viral infections have similar presentation Physical manifestations –redness, edema, exudate in 50% and lymph node enlargement in throat 50

51 Additional Streptococcal Diseases Contact superficial cutaneous diseases –include cellulitis, impetigo, and erysipelas Invasive diseases –may reach underlying muscle 51

52 Superficial Cutaneous Cellulitis –diffuse, spreading infection of subcutaneous tissue –redness and swelling Impetigo –also caused by Staphylococcus aureus –superficial cutaneous infection commonly seen in children –crusty lesions and vesicles surrounded by red border Erysipelas –acute infection of dermal layer of skin –red patches that may occur periodically at same site for years 52

53 Invasive Streptococcal Infections Caused by certain virulent strains of S. pyogenes Rapidly progressive –carry genes for exotoxins superantigens (Select Agent) tissue-destroying protease 53

54 Invasive infections Clinical manifestations –necrotizing fasciitis (“flesh eating”) destruction of sheath covering skeletal muscle –myositis inflammation and destruction of skeletal muscle and fat tissue –toxic shock-like syndrome (TSLS) precipitous drop of blood pressure, failure of multiple organs, and high fever 54

55 Streptococcal Pneumonia Opportunistic pathogen –caused by one’s own normal microbiota Caused by Streptococcus pneumoniae –produces polysaccharide capsule and a toxin –rapidly multiplies in alveolar spaces Disease only occurs in individuals with predisposing condition 55

56 Poststreptococcal Diseases Glomerulonephritis (Bright’s disease) and rheumatic fever 1–4 weeks after an acute streptococcal infection Nonsupportive (nonpus-producing) Most serious problems associated with streptococcal infections in U.S. 56

57 Streptococcal Pneumonia Primary virulence factor –capsule of hyaluronic acid that is anti- phagocytic –allows rapid multiplication of bacteria in alveolar spaces Release of pneumolysin –destroys host cells –alveoli fill with blood cells and fluid 57

58 Streptococcal Pneumonia Diagnosis –chest X-ray, gram stain, culture, and tests for metabolic products Clinical manifestations –abrupt onset of chills, hard labored breathing, chest pain, and rust-colored sputum Treatment, prevention, and control –antibiotic therapy resistant strains have appeared –immunization and treatment of infected persons 58

59 Streptococcal Diseases Other diseases are –sinusitis, conjunctivitis, otitis media –bacteremia, meningitis Treatment, prevention, and control –most treated by antibiotic therapy –Pneumovax capsular vaccine 59

60 Glomerulonephritis Inflammatory disease of renal glomeruli –a type III hypersensitivity Clinical manifestations –edema, fever, hypertension, and hematuria –may spontaneously heal or may become chronic Diagnosis –clinical history, physical findings, and confirmatory evidence of prior streptococcal infection Treatment, prevention, and control –antibiotic therapy (to kill residual bacteria), otherwise no specific therapy 60

61 Rheumatic Fever Autoimmune disease involving heart valves, joints, subcutaneous tissues, and central nervous system Clinical manifestations –vary widely, making diagnosis difficult Treatment, prevention, and control –therapy directed at decreasing inflammation and fever, and controlling cardiac failure –treatment with salicylates and corticosteroids 61

62 Genus Streptococcus Hemolysis patterns used in Lancefield grouping –alpha (  – hemolysis incomplete lysis of red blood cells seen as greenish zone around colony on blood agar –beta (  hemolysis complete lysis of red blood cells seen as clear zone around colony on blood agar 62

63 Hemolysis on blood agar Beta hemolytic (complete) Alpha hemolytic (partial) Gamma hemolytic (none) 63

64 Group B Streptococcal Disease Caused by Gram-positive Streptococcus agalactiae or Group B streptococcus (GBS) Common cause of neonatal and newborn diseases such as sepsis, meningitis, and pneumonia Transmitted directly from person-to-person with many people being transient carriers; vagina may be source for newborns 64

65 GBS Clinical manifestations –early onset disease presents within first few hours after birth may be severe meningitis or death –late onset disease - rare Diagnosis –Gram-positive, beta-hemolytic, streptococcal bacteria growth from cultures of otherwise sterile body fluids Treatment, prevention, and control –detect pregnant carriers –antibiotics 65

66 Important Enterococci and Lactococci Enterococcus faecalis –normal biotic in gastrointestinal tract –opportunistic pathogen (urinary tract infections and endocarditis) –Used as an indicator organism in natural waters, ocean, brackish water, frozen food Lactococcus lactis – production of buttermilk and cheese 66


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